This invention is generally directed to coating processes, and more specifically to the coating of various components in an imaging and printing apparatus. More specifically, the present invention is directed to the coating of ink jet print heads and the like in printing apparatus, which coatings are abrasion resistant and enable the minimization or elimination of undesirable ink drop deflection which can, and in many instances does causes poor image quality. In one embodiment of the present invention the coating selected is comprised of amorphous carbon, also referred to as diamond-like carbon. This material may contain hydrogen, halogen, especially fluorine, mixtures thereof throughout the coating layer or as a layer at the exposed surface of the coating.
Printing methods utilizing ink jet technologies are well known and ink jet printers are commercially available from, for example, Xerox Corporation as the ink jet printer Model 4020.TM.. Also, there is illustrated, for example, in U.S. Pat. No. 4,335,389; 4,392,907 and 4,794,410, the disclosures of which are totally incorporated herein by reference, a particular ink jet printing technology which is based on thermal rather than electrostatic ink acceleration methods. Ink jet printing methods generally involve the physical separation of a predetermined and metered quantity of ink, which could be a dye based or a pigmented fluid material, from an orifice. The specific details of this process, the separation of the fluid ink from its physical surroundings, the ink channel and its orifice, determines to a large extent the direction in which the ink will travel to the paper and thus determine where the mark on the paper will be made. Any microscopic irregularity that would affect the isotropy of this ink-orifice separation process will usually cause the ink to travel in an uncontrolled and not intended direction, that is, for example, not orthogonal to the plane defined by the orifice. This results in poor quality of the images and text that is printed on the paper. The processes of this invention avoid or minimize the aforementioned problem and, more specifically, enables the minimization or elimination of the effects of such microscopic anisotropies of the orifice. In one embodiment of the present invention this is accomplished by the provision of coatings of the exit orifice, which coatings have the property that they repel the ink that is used for the printing process. This repellent property is a quantifiable physical property that is commonly expressed in terms of the contact angle that a small ink droplet forms with this coating. A large contact angle of, for instance, more than 90.degree. indicates a repellent nature of the coating with the ink and smaller contact angles of, for instance, less than 85.degree. indicate that the ink will cover ("wet") the coating. The processes of the present invention provide coating formulations that have a phobic or a shunning property for many dye and water-based ink formulations, including those that are commercially available from E.I. DuPont de Nemours, Inc. One object of the present invention is to provide coatings that are mechanically suitable for the aforementioned coating applications in that the phobic effect is retained and does not wear off for an extended time period in the ink jet printing devices, that is for example wearing can be caused, for example, by chemical reactions or mechanical abrasion even though the coating is continuously or intermittently exposed to the passage of ink drops through the opening. Specifically, the combination of properties of repulsion and extended werability is obtained by the provision of coatings known as diamond-like or amorphous carbon layers. These coatings are substantially composed of carbon containing from about 1 to about 60 percent, and preferably from about 1 to about 40 weight percent, of monovalent elements such as hydrogen, halogen, such as fluorine, chlorine, or mixtures thereof, either homogeneously present throughout the layer or present on the surface of the carbon coating.
Other thermal ink jet printing processes and apparatuses wherein the coatings of the present invention may be selected are illustrated in U.S. Pat. Nos. 4,639,748; 4,864,329 and Re. 32,572, the disclosures of each of the aforementioned patents being totally incorporated herein by reference.
Illustrated in copending application U.S. Ser. No. 504,224, filed on 04/04/90, entitled Surface Hardening of Reprographic Machine Components by Coating or Treatment Processes, the disclosure of which is totally encorporated herein by reference, is a process for maximizing wear resistance of electrophotographic components which comprises coating the components with a diamond-like amorphous carbon material, a titanium compound, or mixtures thereof.